Thermodynamic limits on cell size in the production of stable polymeric nanocellular materials

Estravís, Sergio; Windle, Alan H.; Es, M. van; Elliott, James A.

doi:10.1016/j.polymer.2019.122036

Cited by 5 publications

(5 citation statements)

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“…Regarding the bulk density, it is theoretically proved that closed-cell materials cannot present cell sizes below 10 nm together with low densities. However, open-cell material could lead to combining cell sizes of 20 nm with porosities over 0.9 [113]. Regarding the reduction in solid thermal conductivity, strategies to enhance phonon scattering should be studied.…”

Section: Future Perspectivesmentioning

confidence: 99%

Thermal Conductivity of Nanoporous Materials: Where Is the Limit?

et al. 2022

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Nowadays, our society is facing problems related to energy availability. Owing to the energy savings that insulators provide, the search for effective insulating materials is a focus of interest. Since the current insulators do not meet the increasingly strict requirements, developing materials with a greater insulating capacity is needed. Until now, several nanoporous materials have been considered as superinsulators achieving thermal conductivities below that of the air 26 mW/(m K), like nanocellular PMMS/TPU, silica aerogels, and polyurethane aerogels reaching 24.8, 10, and 12 mW/(m K), respectively. In the search for the minimum thermal conductivity, still undiscovered, the first step is understanding heat transfer in nanoporous materials. The main features leading to superinsulation are low density, nanopores, and solid interruptions hindering the phonon transfer. The second crucial condition is obtaining reliable thermal conductivity measurement techniques. This review summarizes these techniques, and data in the literature regarding the structure and thermal conductivity of two nanoporous materials, nanocellular polymers and aerogels. The key conclusion of this analysis specifies that only steady-state methods provide a reliable value for thermal conductivity of superinsulators. Finally, a theoretical discussion is performed providing a detailed background to further explore the lower limit of superinsulation to develop more efficient materials.

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Section: Future Perspectivesmentioning

confidence: 99%

Thermal Conductivity of Nanoporous Materials: Where Is the Limit?

et al. 2022

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“…The issue of creating nanocells in a polymer foam is directly related to the thermodynamic instability of the nanoscale since the cells are inclined to burst during the foaming process and merge [140]. Therefore, Shi et al [141] project a method and polymeric blend that provides stable cell growth and developing high porosity nanocellular polymer foams.…”

Section: Nanocellular Foamsmentioning

confidence: 99%

Production and Application of Polymer Foams Employing Supercritical Carbon Dioxide

Lima¹,

Bose²

2022

Advances in Polymer Technology

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Polymeric foams have characteristics that make them attractive for different applications. However, some foaming methods rely on chemicals that are not environmentally friendly. One of the possibilities to tackle the environmental issue is to utilize supercritical carbon dioxide ScCO2 since it is a “green” solvent, thus facilitating a sustainable method of producing foams. ScCO2 is nontoxic, chemically inert, and soluble in molten plastic. It can act as a plasticizer, decreasing the viscosity of polymers according to temperature and pressure. Most foam processes can benefit from ScCO2 since the methods rely on nucleation, growth, and expansion mechanisms. Process considerations such as pretreatment, temperature, pressure, pressure drop, and diffusion time are relevant parameters for foaming. Other variables such as additives, fillers, and chain extenders also play a role in the foaming process. This review highlights the morphology, performance, and features of the foam produced with ScCO2, considering relevant aspects of replacing or introducing a novel foam. Recent findings related to foaming assisted by ScCO2 and how processing parameters influence the foam product are addressed. In addition, we discuss possible applications where foams have significant benefits. This review shows the recent progress and possibilities of ScCO2 in processing polymer foams.

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confidence: 99%

“…However, simple geometrical considerations and the physical dimensions of the polymer chains are enough to demonstrate that cell sizes equal to or below 10 nm and low densities cannot be achieved with close-cell geometries [ 27 ]. On the contrary, Estravis et al [ 27 ] proposed that open-cell geometries could offer this possibility, reaching cell sizes below 20 nm and porosities over 0.9 simultaneously if cell strut thicknesses of 1.5 nm are assumed. Although the assumed cell strut thickness could be extremely low (struts or walls below 10 nm have still not been reported, while thicknesses over 20 nm are the most common) [ 25 , 28 ], open-cell nanocellular structures should be further studied aiming to achieve low-density nanocellular foams.…”

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confidence: 99%

“…Recent works have shown the potential of these techniques in the study of nanocellular polymers. Estravis et al [ 27 ] employed MD to analyze the stability of gas–polymer structures in the nanocellular range, finding that the behavior of the internal pressure in the polymer is a key factor in the minimum stable cell size achievable. Moreover, Zhang et al [ 39 ] studied the behavior of ultrathin PMMA films following the same approach, investigating the failure of cell walls during cell growth on nanocellular foams.…”

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confidence: 99%

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